Problem: In math class, the girl to boy ratio is $10$ to $8$. If there are $50$ girls, how many boys are there?
Explanation: A ratio of $10$ girls to $8$ boys means that there is a group of $10$ girls for every group of $8$ boys. If there are $50$ girls, then there are $5$ groups of $10$ girls each. Because we know the ratio is $10:8$ , there must be $5$ groups of $8$ boys each. There is a total of $40$ boys in math class.